Idler rollers are widely used in machinery and conveyors to transfer loads. The rollers may be stud mounted from a rail or other structure where the roller projects in cantilever fashion, or yoke mounted where the stud or shaft is supported at either or both ends. A load bearing roller is mounted on the stud or shaft for rotation using a ball or roller bearing. The roller tread may have a variety of profiles, such as plain, crowned, flanged, V-groove, double V, or U-groove, depending on the application. An example of such idler rollers is the well known LOAD RUNNERS.RTM. brand idler rollers made and sold by The OSBORN Manufacturing unit of Jason Incorporated.
While having excellent load bearing capabilities, such rollers are relatively costly to make and assemble. Care has to be taken to achieve concentricity in press fit operations, and seals or shields are usually required since many idler rollers operate under heavy radial and thrust loads, at high speeds, and in a dirt, sand, or moisture environment.
Some of the drawbacks of conventional idler rollers, whether made with roller, ball, or even bronze sleeve bearings is that they require lubrication. This in turn may create a contamination problem which would limit, for example, food applications. Also any metal material is subject to corrosion or sparking which would limit both the useful life and applications. A lubricated bearing also has temperature limitations. Ball, roller, or some sleeve design bearings also may be rather noisy, not enhancing a factory environment.
With the advent of plastics, particularly plastics which have some degree of lubricity, some manufacturers have been replacing ball or needle bearings with a sleeve construction which utilizes the low coefficient of friction of some plastic materials.
However, such sleeves are usually of a multi-part construction, or may be attached to the interior of a roller by adhesion, or in a similar manner directly to a stud. The more parts, the more wear points and the greater opportunity for dirt or grit to enter between the moving parts, which would soon scour the plastic material. Such bearings have limited useful life and loading characteristics. Also such bearings are hard to make and assemble and maintain concentricity.
It would accordingly be desirable to have the simplicity and low cost of a plastic sleeve bearing construction, without the assembly steps required, and yet have longer life and higher load characteristics. It would also be desirable for the bearing and roller to be of unitary construction, with the outer tread being a integral part of the bearing assembly, eliminating a multiple part construction.